|  | 4.1 | LAN Design Goals and Components
| 4.1.3 |
The function and placement of servers when designing a network
One of the keys to designing a successful network is to understand the function and placement of servers needed for the network. Servers provide file sharing, printing, communication, and application services, such as word processing. Servers typically do not function as workstations; rather, they run specialized operating systems, such as NetWare, Windows NT, UNIX, and Linux. Today, each server usually is dedicated to one function, such as e-mail or file sharing. Servers can be categorized into two distinct classes: enterprise servers and workgroup servers. An enterprise server supports all the users on the network by offering services, such as e-mail or Domain Name System (DNS). E-mail or DNS is a service that everyone in an organization (such as the Washington School District) would need because it is a centralized function. On the other hand, a workgroup server supports a specific set of users, offering services such as word processing and file sharing, which are services only a few groups of people would need. Enterprise servers should be placed in the main distribution facility (MDF). This way, traffic to the enterprise servers has to travel only to the MDF and does not need to be transmitted across other networks. Ideally, workgroup servers should be placed in the intermediate distribution facilities (IDFs) closest to the users accessing the applications on these servers. You merely need to directly connect servers to the MDF or IDF. By placing workgroup servers close to the users, traffic only has to travel the network infrastructure to that IDF, and does not affect other users on that network segment. Within the MDF and IDFs, the Layer 2 LAN switches should have 100 Mbps or more allocated for these servers.
| Threaded Case Study
Washington Project: Server Placement and Function

You should categorize all file servers for the Washington School District as enterprise or workgroup types, and then place servers in the network topology according to the anticipated traffic patterns of users and according to the following functions:

- DNS and E-Mail Services - Each district hub location should contain a DNS server to support the individual schools serviced out of that location. Each school should also contain a host for DNS and e-mail services (that is, a local post office) that will maintain a complete directory of the staff members and students for that location.

- The Administrative Server - Each school location should have an administration server for the student tracking, attendance, grading, and other administrative functions. This server should run TCP/IP as its protocol suite and should be made available only to teachers and staff members.

- The Library Server - The school district is implementing an automated library information and retrieval system for an online curricular research library. This server should run TCP/IP as its OSI Layer 3 and Layer 4 protocol and should be made available to anyone at the school site.

- Application Server - All computer applications, such as word processing and spreadsheet software, should be housed in a central server at each school location.

- Other Servers - Any other servers implemented at the school sites should be considered departmental (workgroup) servers, and should be placed according to user group access needs. An example would be a server running an instructional application for a specific school site.

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